Unicoil electrical indicator instrument

ABSTRACT

A novel electrical instrument or gauge is disclosed for indicating current flow as produced by an external sending unit, for example. The indicator instrument comprises a rotor assembly which includes a pointer and a permanent magnet armature attached thereto, the rotor assembly being disposed for rotation in a plane about a rotational axis. Importantly, a single electromagnetic coil is disposed substantially in said plane and aligned with respect to said rotor assembly such that the center line of said coil intersects with said rotational axis. A magnetized core piece is also disposed substantially in said plane and is aligned with respect to the rotor assembly and the electromagnetic coil such that the center line of the magnetized core piece intersects with the rotational axis of the rotor assembly and lies at an angle of substantially 90* to the center line of said electromagnetic coil. In the preferred inventive embodiment, a further magnetized core piece is disposed within the electromagnetic coil provided, coaxial with the center line thereof. The single or unicoil design of the instant invention is such that the novel assembly exhibits a simplified construction and increased reliability. The operation of the novel instrument of the instant invention is typical in that the pointer will move in accordance with current flow through the electromagnetic coil, which current is itself in accordance with a variable to be indicated.

United States Patent 1 Wible et al.

[4 1 Sept. 4, 1973 1 UNICOIL ELECTRICAL INDICATOR INSTRUMENT [75]lnventors: Joseph B. Wible, Lancaster; Paul E.

Martin, Ephrata, both of Pa.

[73] Assignee: Datcon Instrument Company, East Petersburg, Pa.

[22] Filed: Apr. 6, 1972 [21] Appl. No.: 241,674

[52] US. Cl. 324/146 [51] Int. Cl G0lr 1/20 [58] Field of Search324/146, 147, 151,

[56] References Cited UNITED STATES PATENTS 1,393,737 10/1921 Ballman324/146 1,580,768 4/1926 Todd 2,178,108 10/1939 Schwarze 324/14ORPrimary Examiner Alfred E. Smith Attorney-John C. Holman, Dennis G.Kraft et a1.

[57] ABSTRACT A novel electrical instrument or gauge is disclosed forindicating current flow as produced by an external sending unit, forexample. The indicator instrument comprises a rotor assembly whichincludes a pointer and a permanent magnet armature attached thereto, therotor assembly being disposed for rotation in a plane about a rotationalaxis. importantly, a single electromagnetic coil is disposedsubstantially in said plane and aligned with respect to said rotorassembly such that the center line of said coil intersects with saidrotational axis. A magnetized core piece is also disposed substantiallyin said plane and is aligned with respect to the rotor assembly and theelectromagnetic coil such that the center line of the magnetized corepiece intersects with the rotational axis of the rotor assembly and liesat an angle of substantially 90 to the center line of saidelectromagnetic coil. In the preferred inventive embodiment, a furthermagnetized core piece is disposed within the electromagnetic coilprovided, coaxial with the center line thereof. The single or unicoildesign of the instant invention is such that the novel assembly exhibitsa simplified construction and increased reliability. The operation ofthe novel instrument of the instant invention is typical in that thepointer will move in accordance with current flow through theelectromagnetic coil, which current is itself in accordance with avariable to be indicated.

6 Claims, 2 Drawing Figures 28 36 Aoi e2 '4 I l l l 1 i i i 4 4 .v i l)4, i l 5i 1 131? r PAIENTEDSEP 41913 3.757. 215

In I

I I lul UNICOIL ELECTRICAL INDICATOR INSTRUMENT BACKGROUND OF THEINVENTION This invention generally relates to electrical instruments andparticularly concerns a novel electrical indicator instrument of thetype particularly adapted to measure and indicate current flow.

Electrical indicator instruments of the current measuring or ammetertype under consideration herein are utilized in various environments tomeasure current flow through some external circuit. For example, suchelectrical indicator instruments can be coupled in circuit with a remotesending or transmitting unit, such as a temperature sending device, aliquid level sensing device, or the like, which sending units normallyalter their resistance in accordance with some variable to be indicated.The sender unit itself is usually disposed in electrical circuit with asource of current, such as a battery. Accordingly, the typicalelectrical indicator instrument thereby is energized with current inaccordance with a variable to be indicated, the instrument eitherreading the average value of the current flow therethrough, or theinstantaneous value thereof.

A particular environment of utility for such electrical indicatorinstruments are as panel-type instruments or gauges for use in motorvehicles. In this respect, such instruments would serve to indicate thevalue of a variable such as engine temperature, fuel level, chargingrate, or the like, in accordance with current flow through a respectiveassociated sending unit. Such instruments or gauges that are to beutilized in motor vehicles are subject to more stringent constructionalrequirements. For example, panel-type instruments may be fabricated ofsturdy materials, must be economical to manufacture, and must bereliable in operation due to their oftentimes inaccessible mountinglocations. Conventional panel-type indicating instruments rarely meet orpossess these requisite attributes. For example, the typical panel-typeinstrument normally possesses a plurality of electromagnetic coils and aresultant complex internal magnetic circuit which oftentimes leads to anincreased failure rate and lack of reliability. Additionally, typicalpanel-type instruments normally are provided with a casing which itselfmust be connected to some vehicle ground, this connection being inaddition to separate electrical connections that must be made to thevarious internal electromagnetic coils. Again, complexity in.installation, construction, and operation are evident.

BRIEF SUMMARY OF THE INVENTION It should therefore be apparent, that aneed exists in the electrical indicator instrument art for an improvedinstrument of novel constructional design by which the disadvantages ofprior art designs as above-discussed are eliminated. It is the primaryobjective of the instant invention to provide such an improvedelectrical indicator instrument.

A further, more specific, yet equally important objective of the instantinvention concerns the provision of an electrical indicator instrumentwhich can be inexpensively manufactured and which can be easilyassembled and constructed.

Another objective of the instant invention concerns the provision of anelectrical indicator instrument, particularly adapted for panel mountingin a vehicle, for

example, which does not require any ground connection, but merelyrequires two external connections to a circuit.

Yet another objective of the instant invention concerns the provision ofan electrical indicator instrument of the type described which evidencesan increased reliability over prior art designs.

A still further objective of the instant invention concerns theprovision of an electrical indicator instrument which provides astablized gauge read-out, irrespective of normal voltage fluctuations aswould occur in a modern motor vehicle electrical system.

Yet another objective of the instant invention concerns the provision ofan electrical indicator instrument which provides a so-calledreturn-to-zero feature whereby the indicator thereof will align itselfto some quiescent or zero" point upon deenergization of the instrument.

These objectives as well as others which will become apparent as thedescription proceeds are implemented by the instant invention which, asabove-discussed, comprises an electrical indicator instrument formeasuring current flow therethrough, the instrument in the preferredinventive embodiment measuring the average value of such current flow.The current flow itself is such as would be obtained from a remotesending unit disposed in circuit with a vehicle battery, for example,the instrument adapted to be energized with current in accordance with avariable to be indicated.

The electrical indicator instrument of the instant invention can bethought to consist of three basic components or systems comprising: anexternal electrical circuit; an internal magnetic circuit; and amagnet-pointer assembly which serves to generate the read-out orindication of current flow through the external circuit.

As above-discussed, the external circuit in which the instant inventiveinstrument is contemplated to be utilized comprises a circuit includingthe battery of a motor vehicle, for example, and a remote sending unitadapted to vary its resistance, for example, in accordance with somevariable to be indicated. The battery and the sending unit arecontemplated to be connected in series circuit with the electricalindicator instrument, the instrument itself having only two externalconnections. In this fashion, ground connections typical of electricalindicator instruments of the prior art are eliminated which eliminatesthe need for providing metal panels, metal clamps or special wiring andthus reduces the cost of the novel device.

The magnet-pointer assembly of the novel electrical indicator instrumentcomprises a rotor assembly which will be seen to include a pointer and apermanent magnet armature attached thereto. The rotor assembly isdisposed for rotation in a plane about a rotational axis. Again, eventhe construction of the rotor assembly of the instant invention exhibitsa marked simplification over prior art types in that, as will be seen,the rotor assembly is contemplated to comprise a one-piece injectionmolded plastic pointer assembly.

The internal magnetic circuit of the indicator instrument is likewisesimple in construction. Lying at the heart of the invention is theutilization of but a single electromagnetic coil which is disposedsubstantially in the plane of rotation of the rotor assembly and isaligned with respect to the rotor assembly such that the center line ofthe single electromagnetic coil intersects with the rotational axis ofthe rotor assembly. Rather than utilizing additional electromagneticcoils as do typical prior art constructions, the instant inventioncontemplates the utilization instead of a first magnetized core piecewhich is disposed substantially in the same plane of rotation of therotor assembly and is aligned with respect to the rotor assembly and thesingle electromagnetic coil such that the center line of the core pieceintersects with the rotational axis of the rotor assembly and lies at anangle of substantially 90 to the center line of the electromagneticcoil.

The magnetic circuit of the electrical indicator instrument of theinstant invention is completed by the provision of a second magnetizedcore piece which is contemplated to be actually disposed within theelectromagnetic coil coaxial with the center line thereof. This secondcore piece provides the above-mentioned return-to-zero feature in thatthe magnetic field produced therefrom serves to bias the rotor assemblyto a predetermined position upon deenergization of the singleelectromagnetic coil. Of course, and so as to refine or shape themagnetic field produced in the instrument, soft iron core pieces aredisposed adjacent each of the magnetized core pieces which greatlyfacilitates operation of the device.

In operation, it can initially be presumed that no current flows throughthe single electromagnetic coil of the instrument. In this condition,the magnetized core piece which is disposed within the electromagneticcoil creates a magnetic field which attracts the permanent magnetarmature of the rotor assembly such that the rotor assembly is biased tosome predetermined position, such as zero. As current flows through thesingle electromagnetic coil, the magnetic field produced therebyoperates upon the permanent magnet armature, in association with thepermanent magnetic field operating upon the armature magnet produced bythe first magnetized core piece disposed at an angle of 90 with respectto the electromagnetic coil. As such, the permanent magnet rotor willtend to align itself in accordance with the resultant or combinedmagnetic field vectors produced, on the one hand, by the electromagneticcoil, and, on the other hand, by the first permanent magnet core piece.The position assumed by the armature magnet will be indicated by thepointer attached thereto and thus, the average value of current flowthrough the single electromagnetic coil would be read-out and indicated.

BRIEF DESCRIPTION OF THE DRAWINGS The invention itself will be betterunderstood and further features and advantages thereof will becomeapparent from the following detailed description of a preferredinventive embodiment, such description making reference to the appendedsheet of drawings, wherein:

FIG. I is an exploded perspective view of the electrical indicatorinstrument of the instant invention, the constructional details thereofbeing simplified so as to facilitate an understanding of the' novelconcepts therein disclosed; and

FIG. 2 is a schematic plan view of a typical external circuit and themagnetic circuit associated with the electrical indicator instrument ofthe invention.

DETAILED DESCRIPTION OF A PREFERRED INVENTIVE EMBODIMENT Referring nowto the drawings and particularly to FIG. I thereof, an exploded, thoughsimplified, illustration of the novel electrical indicator instrument ofthe invention can be seen. The instrument comprises a rotor assemblygenerally designated by reference numeral 10 which includes a one pieceinjection molded plastic pointer 12 and a disc-like permanent magnetarmature 14 attached thereto. Permanent magnet 14 is magnetized acrossthe diameter thereof, so as to present opposite magnetic poles onopposite sides. The rotor assembly is pivotally mounted about a spindle16 for rotation in a plane about rotational axis 18.

The novel electrical by instrument further includes a singleelectromagnetic coil generally designated by reference numeral 20. Inthe preferred inventive embodiment, the electromagnetic coil 20comprises a plurality of windings 22 about an internal iron core 24. Thewindings 22 are disposed in the same direction and the end connectionsthereof are respectively coupled to lugs 26 and 28 which extend througha disc-like backing plate generally designated by reference numeral 30as will be discussed in more detail hereinbelow.

The positioning of the electromagnetic coil 20 is such that coil 20 isdisposed substantially in the same plane of rotation of the rotorassembly 10 and is aligned with respect to the rotor assembly such thatthe center line 26' of the electromagnetic coil 20 (see FIG. 2)intersects with the rotational axis 18 of the rotor assembly 10. In thepreferred inventive embodiment, as shown, theelectromagnetic coil 20 ismaintained in the abovedescribed position by means of a bobbin 40, orthe like, disposed on the backing plate 30.

A first magnetized core piece generally designated by reference numeral32 is also disposed substantially in the plane of rotation of the rotorassembly 10 and is aligned with respect to the rotor assembly 10 and thesingle electromagnetic coil 20 such that the center line 34 of themagnetized core piece 32 (see FIG. 2) intersects with the rotationalaxis 18 of the rotor assembly 10 and lies at an angle of substantiallyto the center line 26 of the electromagnetic coil 20. The magnetizedcore piece 32 is maintained in position in substantially the same manneras described with respect to the electromagnetic coil 20 in that abobbin or other suitable mounting 36 is provided on the backing plate30.

Referring, now, specifically to FIG. 2 of the drawings, the detailedconfiguration of the electromagnetic coil 20 and the first magnetizedcore piece 32 can be seen. Specifically, it should be noted thatmagnetized core piece 32 is, in fact, constructed of an internal ironcore 34' which lies in contact with a cylindrical permanent magnet 36,permanent magnet 36 being magnetized along the center line 34 thereof.

Similarly, the electromagnetic coil 20 incorporates an iron core 24, asabove-discussed, as well as a second magnetized core piece 38 which isactually disposed within the coil 20 coaxial with the center line 26'thereof. In a fashion to be explained hereinbelow, this secondmagnetized core piece 38 serves to bias the permanent magnet armature 14of the rotor assembly 10 to a predetermined position, such as a zero"position upon deenergization of the electromagnetic coil 20.

In the preferred inventive embodiment, soft iron core pieces 34', 24 aredisposed adjacent, or in magnet circuit, with each of the magnetizedcore pieces 36 and 38. These soft iron core pieces 34, 24 serve to shapethe generated magnetic field. As another fine point of construction, thepreferred inventive embodiment is such that the positions of amagnetized core piece 38 and the core piece 24 disposed in the coil areadjustable, i.e., adjustably disposed to be moved in the direction oftheir respective center lines. This particular feature of the instantprovidd insures that the novel instrument can be calibrated andelectrically matched to an external sender. 55

The novel instrument assembly further includes a housing thereforpreferably constructed of plastic. As shown in FIG. 1, the housing is oftwo-part construction and includes a hollow annular casing generallydesignated by reference numeral 42 which is open at both ends thereof. Atransparent window 44 which may, for example, contain indicia thereon,is disposed over one of the ends of the housing. The manner in which thebezel 46 is attached to the annular casing 42 in itself represents asimplification of prior art construction. Specifically, and in thepreferred inventive embodiment, a mold is provided and the bezel 46 isdisposed in the mold. The annular casing 42 is then injection molded byforcing plastic into the mold thus bonding the metal bezel with thecasing 42. Of course, and if desired, other techniques could be utilizedfor bonding the bezel 46 to the casing 42 and, in fact, the bezel 46could itself be constructed of plastic. 66

The housing further includes a disc-like backing plate asabove-discussed. The backing plate 30 has been seen to carry the rotorassembly 10, the electromagnetic coil 20 and the various core pieces 32and 24 mounted thereon. Since all the internal parts of the electricalindicating instrument are disposed on the backing plate or disc 30,assembly and/or repair of the apparatus is facilitated. The backingplate 30 is itself attached to the other open end of the annular casing42, preferably by a technique such as ultrasonic welding.

Referring again to FIG. 2 of the appended drawings, a typical externalcircuit into which the novel instrument is placed is disclosed. Asmentioned at the outset, the electrical indicating instrument isparticularly adapted for use as a panel-type gauge or meter in a motorvehicle, for example. Accordingly, the external circuitry will be seento include a DC battery 48, one terminal of which is connected toground, as shown. The other terminal of battery 48 is coupled through anignition switch 50, for example, to one end of the winding 22 of theelectromagnetic coil 20. The other end of the winding 22 of coil 20 isconnected in series circuit to a remote sender unit 52, which senderunit could comprise a temperature sending device or the like, senderunit 52 likewise being connected to ground to complete the seriescircuit. As also shown in FIG. 2, the remaining circuitry normallyassociated with a motor vehicle, for example, is connected to the seriescircuit above-described to either end of the ignition switch 50. Thus, aregulator circuit might be connected to the positive terminal of battery48, whereas other accessory circuits and the like could be connected onthe gauge side of the ignition switch 50.

Operation of the electrical indicator instrument is as follows. When thecoil 20 is deenergized, the pennanent magnet core piece 38 thereofprovides a magnetic field which serves to attract the permanent magnetarmature 14 of the rotor assembly 10 so that the pointer 12 of the rotorassembly assumes a predetermined, or zero position. This is a so-calledretum-to-zero" operational feature. oftentimes, users of the instrumentor gauge are desirous of having the pointer return to a zero or safetyposition when power is removed so that, upon reenergization of theinstrument, the pointer motion can be observed so as to indicate aproper connection or lack of fault in the external electrical circuit.

When current is flowing in the external circuit from battery 48, theresistance of the remote sender unit 52 determines the magnitude of suchcurrent. Since the windings 22 of coil 20 are disposed in series circuitwith this current path, a magnetic field will be produced by theelectromagnetic coil 20. This magnetic field will interact with themagnetic field effected by the magnetized core piece 32 so that aresultant magnetic field vector will appear. Since the permanent magnetarmature 14 of the rotor assembly 10 is magnetized across its diameter,this armature will track the resultant magnetic field vector andspecifically, will attempt to align its poles in the direction of themagnetic field vector at all times. In this manner, the permanent magnetarmature 14 will cause the pointer 12 to which it is attached toindicate the magnitude of the current flow through the circuit, or themagnitude of the remote sender 52 resistance change by means of changesin the direction of the resultant magnetic field vector.

In addition, the novel electrical indicator instrument design of theinstant invention provides a freedom from the influence of normal inputvoltage variations such as would occur in a vehicle electrical system.Specifically, since these normal input voltage variations are small dueto the characteristics of above described. ignition system design, theutilization of the single electromagnetic coil provides sufficientenough regulatory characteristics, without the necessity of a dual coildesign so typical in the prior art.

Calibration of the electrical indicator instrument of the instantinvention can readily be effected simply by adjusting thecharacteristics of the magnetized core pieces and, specifically, bymoving the magnetized core pieces 32 and 38 in a direction along theirvarious center lines thereof as above described. Final calibration,during production, could thereby be provided by replacing the remotesender 52, for example, with known resistor values. Additionally, and ifdesired, the instrument can include an internally mounted fixed carbonresistor, or the electromagnetic coil 20 could be wound with specificsizes of resistance wire, so as to achieve a matched condition foroptimum instrument sensitivity, thus matching various families of remotesenders 52 with a particular instrument.

It should now be apparent from the foregoing detailed description thatthe objects set forth at the outset to this specification have beensuccessfully achieved. Moreover, while there is shown and described apreferred embodiment of the invention, those skilled in the art shoulddistinctly understand that the invention is not limited specificallythereto but may be otherwise variously embodied and practised within thescope of the following claims. Accordingly,

What is claimed is:

1. An electrical indicator instrument comprising in combination:

a rotor assembly including a pointer and a permanent magnet armatureattached thereto, said rotor assembly being disposed for rotation in aplane about a rotational axis;

a single electromagnetic coil disposed substantially in said plane andaligned with respect to said rotor assembly such that the center line ofsaid coil intersects with said rotational axis;

a first magnetized core piece disposed substantially in said plane andaligned with respect to said rotor assembly and said electromagneticcoil such that the center line of said first core piece intersects withsaid rotational axis and lies at an angle of substantially 90 to saidcenter line of said electromagnetic coil;

a second magnetized core piece disposed within said electromagnetic coilcoaxial with the center line thereof, said core piece biasing said rotorassembly to a predetermined position upon deenergization of saidelectromagnetic coil; and

electrical connections to said electromagnetic coil by which said coilis adapted to be energized with current in accordance with a variable tobe indicated.

2. An instrument as defined in claim 1, wherein said core pieces areadjustably disposed to be moved in the direction of their respectivecenter lines, whereby the instrument can be calibrated and electricallymatched to an external sender.

3. An instrument as defined in claim 2, further including soft iron polepieces disposed adjacent said magnetized core pieces to shape themagnetic field.

4. An instrument as defined in claim 3, wherein each magnetized corepiece is a permanent magnet cylindrical core magnetized along the centerline thereof, and wherein said permanent magnet armature is of disc-likeconstruction and is magnetized across the diameter thereof.

5. An instrument as defined in claim 1, further including a housingtherefor, said housing being constructed of plastic and including ahollow annular casing open at both ends thereof, a transparent windowdisposed over one of the ends of the casing, and a disclike backingplate upon which said rotor assembly, said coil, and said core piecesare mounted, said backing plate being disposed over the other end ofsaid casing.

6. An instrument as defined in claim 1, further including an externalcircuit therefor, said circuit comprising a battery and a sender unitadapted to vary its resistance in accordance with a variable to beindicated, and means connecting said battery, said sender unit and saidelectromagnetic coil in series circuit.

1. An electrical indicator instrument comprising in combination: a rotorassembly including a pointer and a permanent magnet armature attachedthereto, said rotor assembly being disposed for rotation in a planeabout a rotational axis; a single electromagnetic coil disposedsubstantially in said plane and aligned with respect to said rotorassembly such that the center line of said coil intersects with saidrotational axis; a first magnetized core piece disposed substantially insaid plane and aligned with respect to said rotor assembly and saidelectromagnetic coil such that the center line of said first core pieceintersects with said rotational axis and lies at an angle ofsubstantially 90* to said center line of said electromagnetic coil; asecond magnetized core piece disposed within said electromagnetic coilcoaxial with the center line thereof, said core piece biasing said rotorassembly to a predetermined position upon deenergization of saidelectromagnetic coil; and electrical connections to said electromagneticcoil by which said coil is adapted to be energized with current inaccordance with a variable to be indicated.
 2. An instrument as definedin claim 1, wherein said core pieces are adjustably disposed to be movedin the direction of their respective center lines, whereby theinstrument can be calibrated and electrically matched to an externalsender.
 3. An instrument as defined in claim 2, further including softiron pole pieces disposed adjacent said magnetized core pieces to shapethe maGnetic field.
 4. An instrument as defined in claim 3, wherein eachmagnetized core piece is a permanent magnet cylindrical core magnetizedalong the center line thereof, and wherein said permanent magnetarmature is of disc-like construction and is magnetized across thediameter thereof.
 5. An instrument as defined in claim 1, furtherincluding a housing therefor, said housing being constructed of plasticand including a hollow annular casing open at both ends thereof, atransparent window disposed over one of the ends of the casing, and adisc-like backing plate upon which said rotor assembly, said coil, andsaid core pieces are mounted, said backing plate being disposed over theother end of said casing.
 6. An instrument as defined in claim 1,further including an external circuit therefor, said circuit comprisinga battery and a sender unit adapted to vary its resistance in accordancewith a variable to be indicated, and means connecting said battery, saidsender unit and said electromagnetic coil in series circuit.